The invention relates to the field of non-destructive testing. More specifically, the invention relates to the use of transmitted waves (e.g., ultrasonic) to make specific determinations regarding an object through which the wave passes.
Non-destructive testing using ultrasonic waves is widely used in a number of testing environments, including the construction industry. For example, ultrasound testing techniques provide accurate grading of construction material, which in turn allows a builder to match the strength of the construction member to the type of construction project. In addition, proper grading permits manufacturers of the construction material, like sawmills for wooden members, to charge a premium for stronger members, while dedicating weaker members for more appropriate tasks.
In general, non-destructive testing systems operate by transmitting an ultrasonic wave of known characteristics through an object. The various anomalies of the material act upon the transmitted ultrasonic wave and modify its characteristics. The non-destructive testing system then collects the modified wave. By comparing the modified wave with its original form, or with a wave passing through a xe2x80x9cstandardxe2x80x9d or xe2x80x9cidealxe2x80x9d material, the non-destructive testing system is able to detect the various anomalies in the object. Moreover, the non-destructive testing system may be able to determine the type of anomaly, its location in the material, and its effect on the strength of the material.
To date, the process of comparing and analyzing the modified ultrasonic wave in order to detect anomalies has required the consideration of a number of the transmitted and collected characteristics or parameters of the waves. In fact, the necessary parameters usually vary depending on the material being tested. For example, because wooden members (e.g., trees, logs, cants, lumber, engineered and finished wood products) are highly non-homogeneous objects, causing severe distortion of the ultrasonic wave as it passes through, a greater number of parameters are necessary to determine the existence of, and to delineate the boundaries of defects in the wood (e.g., splits, knots, and grain distortions). These parameters may include a time-of-flight (or transmission time) of the ultrasonic wave through the wood member, energy, frequency, and other higher-order statistics statistical parameters. These higher order parameters can be used to describe the position (i.e., the centroid), shape (i.e., the skew) and distribution (i.e., kurtosis) of the waveform. A number of patents and publications discuss the parameters that may be used for defect recognition, as well as how specific conditions influence these parameters, including: Beall, F. C., et al., xe2x80x9cWood: Acoustic Emission and Acousto-Ultrasonic Characteristicsxe2x80x9d Concise Encyclopedia of Materials Characteristics, R. W. Cahn and Eric Lifshin, Eds. Pergammon Press, pp. 551-554, (1993); R. W. Cahn and Eric Lifshin, xe2x80x9cConcise Encyclopedia of Materials Characteristicsxe2x80x9d eds. Pergammon Press, pp. 551-554, (1993); Beall, Frank C., xe2x80x9cOverview of Acousto-Ultrasonics Applied to Wood and Wood-Based Materialsxe2x80x9d, Topical Conference Proceedings Book, Second International Conference on Acousto-Ultrasonics, Atlanta, Georgia, Jun. 24-25, 1993, pp. 153-161; U.S. Pat. No. 5,760,308, entitled xe2x80x9cMethod and apparatus for non-destructively detecting hidden defects caused by bio-deterioration in living trees and round wood materialsxe2x80x9d; and U.S. Pat. No. 5,804,728 xe2x80x9cMethod and apparatus for non-intrusively detecting hidden defects caused by bio-deterioration in living trees and round wood materials.xe2x80x9d In addition, Kiernan, M. T., et al., xe2x80x9cPC Analysis of an Acousto-Ultrasonic Signalxe2x80x9d, Materials Evaluation, 46, pp. 1344-1352, September 1988, provides a comprehensive description of acousto-ultrasonic parameters. Also, in U.S. Pat. No. 6,029,522 to Schafer and Ross, entitled xe2x80x9cUltrasonic Apparatus for Characterizing Wooden Members,xe2x80x9d in which the present inventor is a co-inventor, two parameters, insertion Loss and pulse length, are collected and an independent anomaly detection analysis is conducted on each.
These current approaches, however, are restricted in their limited scope either by focusing on a single anomaly with limited parameters, or by requiring the concurrent examination of multiple parameters to determine the existence of, or delineate the boundaries of the anomalies in the object. In particular, the current techniques have failed to provide a single and robust parameter that provides anomaly detection capability, flexibility in the type of anomaly detected, relative immunity to non-anomaly signal changes (i.e., noise), and flexibility in additional signal processing approaches that permit the detection device to be xe2x80x9ctunedxe2x80x9d to certain anomalies.
Therefore, it would be advantageous to provide a system for detecting anomalies in an object that uses a single flexible parameter. The parameter should not only reliably indicate anomalies, but also it should be relatively immune to other changes in signal conditions caused, for example, by variations in contact pressure, or other insignificant variations in the object itself. That is, the parameter should show some specificity for defects and immunity from xe2x80x9cnoise.xe2x80x9d
The invention describes a method and system for detecting anomalies in a material. The method comprises the steps of transmitting waves through the object, receiving the waves after passage through the object, determining more than one reference characteristic, measuring more than one characteristic of the received wave, comparing a first reference characteristic with a first characteristic of the received wave to create a first factor, comparing a second reference characteristic with a second characteristic of the received wave to create a second factor, combining the first factor with the second factor to create a defect index, and identifying a location of one or more anomalies in the object using the defect index. The step of determining the reference characteristics may comprise transmitting another wave of known characteristics through a material free of anomalies to produce a standard wave, and measuring one or more characteristics of the standard wave. Alternatively, the step of determining the reference characteristics may comprise calculating the reference characteristics from known values of the transmitted wave. The method may further comprise the steps of moving the object such that another portion of the object may be interrogated by the waves. The reference characteristics may then be stored in a computer for further comparison with other received waves. Also, the method may further comprise outputting the locations of the identified anomalies to a grading apparatus for grading the object, or to a device that cuts the object.
The system for detecting anomalies in an object in accordance with the invention comprises a waveform generator that creates waves with one or more characteristics, a transmitting transducer in communication with the ultrasonic waveform generator that transmits the waves through the object, a receiving transducer that receives the waves after passage through the object, and a computer in communication with the receiving transducer and the transmitting transducer. The computer stores reference characteristics and compares a first reference characteristic with a first characteristic of the received wave to create a first factor. The computer also compares a second reference characteristic of with a second characteristic of the received wave to create a second factor. The computer then combines the first factor with the second factor to create a defect index. The computer then identifies a location of one or more anomalies in the object using the defect index. The system may further comprise a display device in communication with the computer, such that the display device displays a graphical map of one or more anomalies within the object. The system may further comprise a conveyor device that moves the object between the transmitting transducer and the receiving transducer. A positional encoder may be in communication with the conveyor device and the computer, such that the positional encoder provide the computer with a position of the object with respect to the transmitting transducer and the receiving transducer. In one embodiment, the object may comprise wood and be interrogated by ultrasonic waves.
Further benefits and advantages of the present invention will become more apparent in the detailed description provided below.